What is a REST API?
A REST API (Representational State Transfer Application Programming Interface) is an architectural style for designing networked applications that use HTTP as the communication protocol. Introduced by Roy Fielding in his 2000 doctoral dissertation, REST defines a set of constraints that, when followed, produce systems that are scalable, stateless, and cacheable. REST APIs have become the dominant approach for building web APIs due to their simplicity and alignment with how the web already works.
Core REST Principles
REST is built around several key constraints. Statelessness means each request from a client contains all the information the server needs to process it, with no session state stored on the server between requests. A uniform interface requires that resources are identified by URIs, manipulated through standard HTTP methods (GET, POST, PUT, PATCH, DELETE), and represented in standard formats like JSON. The client-server separation ensures that the user interface and data storage concerns evolve independently. Cacheability allows responses to be marked as cacheable or non-cacheable, reducing the need for repeated server interactions.
Designing RESTful Endpoints
RESTful API design uses resource-oriented URLs and HTTP methods to express operations. For example, GET /users retrieves a list of users, POST /users creates a new user, GET /users/123 retrieves a specific user, PUT /users/123 replaces that user's data, and DELETE /users/123 removes the user. Query parameters handle filtering, sorting, and pagination (e.g., GET /users?role=admin&page=2). This predictable structure makes REST APIs intuitive for developers and easy to document.
REST in the Modern API Landscape
While REST remains the most widely used API architecture, alternatives like GraphQL and gRPC have gained traction for specific use cases. GraphQL addresses REST's tendency toward over-fetching or under-fetching data by letting clients specify exactly what fields they need. gRPC offers superior performance for internal microservice communication through binary serialization and HTTP/2. Many organizations use REST for public-facing APIs while adopting these alternatives internally where their strengths are most beneficial.